Error of relativistic effective core potentials for closed-shell diatomic molecules of p-block heavy and superheavy elements in DFT and TDDFT calculations.

This article focuses on evaluating the accuracy of small-core energy-consistent Stuttgart/Koln pseudopotentials (PPs) in density functional theory (DFT) and time-dependent DFT (TDDFT) calculations for heavy and superheavy p-block diatomic molecules, including the effects of spin–orbit coupling (SOC). By comparing results for bond lengths, harmonic frequencies, dissociation energies, and vertical excitation energies with those obtained from all-electron calculations using the Dirac–Coulomb (–Gaunt) Hamiltonian, the study finds that PPs yield ground-state and excited-state properties in close agreement with all-electron methods, with slightly larger deviations when SOC is included. The errors associated with PPs are generally small, insensitive to the choice of exchange-correlation functionals, and remain within acceptable ranges (often below 0.1 eV for excitation energies), supporting the reliability of these pseudopotentials for computational studies of heavy and superheavy p-block molecules.